1. Field of the Invention
The present invention relates generally to a storage apparatus for recording/reproducing information to/from a magnetic disk medium, and more particularly to a storage apparatus for a high speed data transfer, mounted with a head IC on its actuator side which connects to its fixed side by way of a flexible printed circuit.
2. Description of the Related Arts
Recent magnetic disk apparatuses tend to have a remarkably increased recording density. This needs a higher data transfer speed. FIG. 1 illustrates a conventional magnetic disk apparatus having a transmission system for read signals and write data in the form of a bidirectional transmission cable 206 of 1 to 2 meters in length connecting a head disk assembly (HDD) 200 and a control board 202 within a gate attached to a rocker. The head disk assembly 200 is provided with a head actuator for positioning a plurality of heads relative to a plurality of magnetic disks rotated by a spindle motor. The head actuator has a plurality of arms carrying at their extremities a plurality of magnetic heads 212-1 to 212-n for read and write and serves to position the magnetic heads 212-1 to 212-n by a voice coil motor (VCM). Between the head actuator and a circuit board 218 on the fixed side there are interposed a plurality of flexible printed circuits (hereinafter, referred to as FPCs) 214-1 to 214-n each having a predetermined length required for a motion of the actuator and having connectors 216-1 to 216-n for the connection to the circuit board 218. For this reason, the heads 212-1 to 212-n and the circuit board 218 are connected to one another by way of a differential signal line pattern (balanced line pattern) on the FPCs 214-1 to 214-n for the bi-directional transmission of analog read signals and digital write data.
The head ICs 210-1 to 210-n are mounted on the FPCs 214-1 to 214-n, respectively, attached to the arms of the head actuator. The head ICs 210-1 to 210-n incorporate a write amplifier for switching the polarity of a recording current through the magnetic heads 212-1 to 212-n in response to write data, and a preamplifier for amplifying a read analog voltage from the heads 212-1 to 212-n. The transmission lines from the head ICs 210-1 to 210-n are connected to one another in parallel on the circuit board 218. The circuit board 218 is provided with terminating resistors 220 and 222 for write data transmission and with a series circuit consisting of an inductance 226 and a resistor 228, for compensating for the frequency characteristic upon the read signal transmission. The circuit board 218 is connected to a read channel on the control board 202 by way of the bi-directional transmission cable 206. A sending/reception end on the read channel is provided with terminating resistors 230 and 232 for read signal transmission and with a driver 204 and a receiver 205.
With the increase in the data transfer speed, such a conventional magnetic disk apparatus requires a broader frequency band of the analog read signal. If the frequency band of the read signal is not broadened, a distortion in the waveform attributable to the attenuation of the high-frequency components may occur, preventing a correct reading, resulting in a reduction of the reproducing margin and hence in a reduction in the data reliability. A barrier to a broader read signal band is a degradation of the frequency characteristics attributable to the stray capacitance occurring between the transmission lines formed on the FPC 214-1 to 214-n and attributable to the stray capacitance occurring between the transmission lines and the ground. The FPC 214-1 to 214-n need a predetermined length for allowing a motion of the actuator, posing a limitation to the reduction of the electrostatic capacity. An output circuit of the preamplifier incorporated in the head ICs 210-1 to 210-n uses an open collector type differential amplifier as a driver for driving the bi-directional cable 206. However, this allows a connection of a plenty of stray capacitance parasitic on the wiring pattern of the FPC 214-1 to 214-n since the fixed side circuit board 218 bears a multiplicity of parallel-connected transmission lines from the FPC 214-1 to 214-n. This stray capacitance causes a remarkable degradation of the frequency characteristics of the analog read signal. In order to compensate for the degradation of the frequency characteristics attributable to the FPC 214-1 to 214-n, the inductance 226 and the resistor 228 are connected to each other in series between the transmission lines of the circuit board 218. In case of receiving the write data from the driver 204 of the control board 204, this compensation circuit may cause a reflection attributable to the mismatching of the impedance and deteriorate the write data transmission characteristics, posing a limitation to the improvement of the data transfer speed. It is also conceivable to change the output circuit of the preamplifier provided in the head IC 210-1 to 210-n from the high impedance open collector type to the low impedance emitter follower type subjected to less influence of the stray capacitance. However, this emitter follower type suffered from a problem that oscillation often takes place when a capacitive load is driven. The stray capacitance impairing the broadening of the read signal band may exist in not only the FPC 214-1 to 214-n provided on the disk head assembly 200 serving as the sending end of the bi-directional transmission cable 206 but also in the input circuit portion of the control board 202 serving as the reception end of the bidirectional transmission cable 206, allowing the stray capacitance at the receiving end to cause a further degradation of the frequency characteristics of the read signals.